Osmoregulation, cellular adaption to changes in osmotic strength of the environment, is a process of fundamental importance for microorganisms, plants, and animals. Our research is focused on the mechanism of osmotic tolerance in microorganisms. We have recently found that enteric bacteria such as E. coli, Salmonella and Klebsiella are markedly protected against osmotic stress by exogenously supplied glycine betaine or its precursor, choline. The name "osmoprotectants" has been proposed for these molecules. A set of genes located near the lac operon of E. coli is required for osmoprotection by choline. These genes, referred to as bet, govern update and conversion of choline to glycine betaine, a potent osmoprotectant. The specific research goals include: i) mapping of bet genes with respect to lac and codAB markers on the E. coli chromosome; ii) biochemical analysis of deletion mutants for choline update, choline oxidase, and betaine aldehyde dehydrogenase activities; iii) molecular cloning analysis of the bet region; iv) mechanism(s) of regulation of bet system by envZ gene and the anesthetic, procaine. The long-range goal of this research is to develop an indepth knowledge of the mechanism of osmotic tolerance in bacteria. The bet genes conferring high levels of osmotic tolerance offer a new approach to this field. There is increasing interest in potential applications of this research in medicine and agriculture.